Posted
by
Soulskillon Friday June 11, 2010 @12:14PM
from the put-it-in-a-michael-bay-movie dept.

KentuckyFC writes "The critical concept that makes a black hole black is the event horizon: a theoretical boundary in space through which light and other objects can pass in one direction but not the other. Since light cannot escape the event horizon, it must be black. The event horizon is a nuisance to astrophysicists because it hides the interesting new physics that must go on inside a black hole. What they would like is a way to get rid of the event horizon so that they can see what goes on behind it. It turns out that just such a thing may be possible, say physicists. According to the mathematics of general relativity, the event horizon should disappear if a black hole were fed enough charge and angular momentum relative to its mass. However the calculations are so fiendish (PDF) that nobody knows whether the black hole would shed this extra angular momentum and charge before it could settle into a stable 'naked' state. However, the possibility that the event horizon could be destroyed raises the question of what astrophysicists would see behind this veil. According to some, black holes are regions of spacetime with infinite curvature called singularities. Many believe that 'naked' singularities cannot exist in nature. And yet there are enough question marks to suggest that this mystery is far from settled."

I would have thought that telling the world things that he knew to be outright lies would have taken some massive balls. And he played it to the hilt, all the way through, even as it all came down around his head. Oh, right, that's not big balls, that's just insanity. My mistake.

Isn't the event horizon the point at which the gravitational pull of a black hole becomes so powerful that not even light can escape? How on earth will feeding the black hole more mass make the event horizon go away? I thought more mass meant more gravity..

(Disclaimer: I Am A Physicist, but this is not my area of expertise, and only the experts understand those equations.)

It's not feeding it mass that does the trick; it's feeding it charge and angular momentum. The only reason you feed it more mass is because you need mass to carry the charge and momentum into the hole.

What you get if you feed it charge and angular momentum is a spinning monopole. I think they are postulating that a spinning monopole causes rotational frame dragging [wikipedia.org], and if you do it right you can get the charged frame dragging effects to cancel out the gravitational effects -- namely, the event horizon.

After you do all that, what will be left? Like the article says, nobody knows. That's why it's exciting.

There are people who think you are joking, and that is my best guess. The problem with your joke (if it is a joke) is that there are actually people who think there is something racist about using the word "black" in the term "black hole". I believe that there was a story on here about that one to two years ago (no, I'm not going to go search for it). Even if it wasn't on here, there was such a story in that time frame.

I once read a bit about black holes, and one of the things I read was: a black hole doesn't necessarily have to be very dense. It can also be sparse (and the larger, the sparser it can be). For example, if you'd take a lot of stars and planets, and put them together (but not too close together), then at one point if you make this large enough, it'll also be a black hole: there appears an event horizon around all this matter. But inside of it are still stars with gaps between them, maybe some planets orbiting around them,... So now I wonder, if the above is true: can someone live inside that? Would there be any noticeable difference between being inside of that, and the other side (the outside) of this event horizon?

I think Slashdot had an article a few months ago, regarding a new theory that hypothesized our known universe actually existing within a giant black hole. Or was it inside a wormhole? It might have been the latter, given that black holes are, by definition, exceedingly dense. I've never heard of "sparse" black holes before, since they have to be dense in order to form in the first place.

One of the problems with approaching a black hole (aside from massive amounts of radiation around ones actively eating matter) is the fact that the force of gravity increases as you approach the mass responsible for the gravity.

With small black holes, as you approach (feet first) the difference in gravitational pull at your feet would be many times larger than the gravitational pull at your head. You would be literally ripped apart, down to the molecular level. This is known as "Spaghettification".

However, with a large enough black hole, you should be able to pass the event horizon before these tidal forces grow large enough to rip you apart. Of course, this does you no good, because once you are inside the event horizon you cannot exert a great enough force to prevent yourself from falling deeper until the forces ARE great enough to rip you apart.

But for a large black hole, in theory, you could cross the event horizon without being ripped apart.

It is assumed that you are falling into the black hole accelerating according to the force of the gravitational pull of the black hole. So you WILL pass through the event horizon in a heartbeat.

Think of it this way:

Even if you had a magical platform that you could stand on just/outside/ the event horizon, you'd still be dead. The amount of gravity pulling down on your would not just stop your blood from flowing upwards, it would crush you into a puddle of goo on the platform.

You're bringing horribly naive Newtonian physics into a realm they do not belong in. Stop before you make yourself sounds like even more of a fool.

As you fall into a black hole the event horizon appears to move away from you from your point of view. An external observer on the other hand would never see you cross the horizon due to other effects, just see you falling ever more slowly into it as the light from you takes ever longer to reach them. You'd see some odd effects from crossing the event horizon but you'd continue to observe things.http://casa.colorado.edu/~ajsh/singularity.html [colorado.edu]http://jila.colorado.edu/~ajsh/insidebh/schw.html [colorado.edu]

The event horizon is precisely the point at which you will be traveling at the speed of light...

No it's not. Matter cannot go at the speed of light and never does. Nothing can go faster than light. That's the whole bloody point of relativity. Stop watching bad sci-fi movies. There are I believe odd effects for certain observers who might see you but practically speaking you'd just be moving at just something like 0.99c. But that's just due to the acceleration of the black hole and it will continue to increase even after you cross the event horizon.

As soon as the flashlight passes through the event horizon, it'll disappear: not even the light from it will be able to reach you.

Nope, you continue seeing the flashlight. Well in some way at least. The event horizon for you has receded. Another way to think of it is that while the light is no longer moving towards you, sort of hovers at the event horizon, you're now moving towards the light. Relative velocity is all that matters. You'll get some odd relativistic distortions I believe, makes me wonder if a human nervous system even survive them, but you'll continue to observe things that went before you through the even horizon.

If you go inside the event horizon (i.e. where we can't see what's going on), regardless how big the black hole is, it is still inevitable that what goes in, must continue going in until it approaches the singularity, or whatever is there where our laws of physics break down. I use to look at the event horizon as something that is per definition the border where things mustn't go in, and where it must. So I don't think that environment is stable enough for life to thrive in; it'd inevitably enter the singul

It seems to me that in order for an established orbit to exist on the event horizon, the orbiting matter would have to be going at the speed of light. I would further presume that any matter orbiting within the event horizon would have to be/exceeding/ the speed of light.

To my knowledge, matter cannot travel at or beyond the speed of light.

The event horizon can be thought of as a photon gas where the photons "orbit" at the speed of light. My philosophical position is that <hand-waving>all the matter is converted into energy at the event horizon due to the extreme physics going on</hand-waving>, so the black hole itself is just a photon gas and everything in it travels at c.

If you were inside a black hole you'd probably see crazy stuff happening like the universe expanding at an ever faster rate and all your calculations about the total mass of the universe that are derived from observing velocities over periods of time would be way off.

I once read a bit about black holes, and one of the things I read was: a black hole doesn't necessarily have to be very dense. It can also be sparse (and the larger, the sparser it can be). For example, if you'd take a lot of stars and planets, and put them together (but not too close together), then at one point if you make this large enough, it'll also be a black hole: there appears an event horizon around all this matter. But inside of it are still stars with gaps between them, maybe some planets orbitin

I thought that the event horizon of a black hole was caused by the immense gravity of the main body. Just an area of space around the black hole where light would be unable to maintain enough momentum to escape the gravitational pull of the singularity.
I don't even want to try understanding the calculations that this theory was derived from. If you were able to remove the event horizon, would that not mean that you would be destroying the singularity itself?

The singularity is a lie. By which I mean, it's not as if this mass is all really in one infinitesimal dot...it's just that you do any characterization of that mass when even light can't escape. So no, you wouldn't be destroying the singularity since we don't really know that's what it is, but, if they do happen to change the black hole by adding charge and angular momentum, and it allows radiation to escape it will cease to be a black hole.

I would like to find a black hole that's just barely massive enough and then try this.

Finally, I think they're just trying to do a thought experiment whereby they change the shape or topology of the event horizon. Imagine a toroidal event horizon for example.

Try not to think of it in terms of light trying to escape in a straight line and just not being strong enough to do it. Instead, think of the straight line as not being straight. Gravity wells curve space-time (a Google Images search for "spacetime" will yield some familiar diagrams of spheres resting on a fabric), and the event horizon of a singulatiry is the point in that curvature where it's so "steep" that it curves back in upon itself. This is difficult to show in the aforementioned diagrams, because it's less about the picture and more about the math behind it.

Basically, from behind the event horizon it's impossible to escape not because you don't have enough force to get away but because all paths lead back to the singularity.

If somebody with more knowledge/expertise on the subject can correct/elaborate, please do.

If you were able to remove the event horizon, would that not mean that you would be destroying the singularity itself?

No. The only reason the event horizon exists is because gravity is pulling so hard that light can't escape. If you were to alter the system so that the pull of gravity is weaker, or is offset by some sort of relativistic frame dragging effect (which is I think what they're postulating here), then the event horizon could disappear while the singularity remains.

Think of the classic space-time fabric picture, where a black hole is an infinite vortex punched down through the fabric. They're pushing the fabri

We always hear about singularities necessitating event horizons, but the converse is most certainly not true. An event horizon may exist without a singularity inside of it.

It depends on scale more than anything. Small black holes almost certainly require a singularity, but a black hole the mass of a galactic cluster actually has a very low average density. So while at the event horizon space-time is very much distorted, on the inside it may not be distorted enough to overcome common everyday forces (the trick of treating a collection of mass as a point source of force doesnt work from inside that collection of mass)

but a black hole the mass of a galactic cluster actually has a very low average density. So while at the event horizon space-time is very much distorted, on the inside it may not be distorted enough to overcome common everyday forces (the trick of treating a collection of mass as a point source of force doesnt work from inside that collection of mass)

Now my brain hurts, could we already be inside an enormous black hole?

A black hole with the wikipedia mass has an event horizon radius of approximately 1.9E+26 meters. Compare with the radius of the observable universe, which is umm.. approximately 1.3E+26 meters. In other worse, if the wikipedia mass is correct, then we are inside a black hole assuming that the Schwarzschild equation for calculating event horizons is correct. I think the existance of dark energy has changed the game tho, such that we certainly cont be confident of the Schwarzschild radius calculation at such large scales.

The Schwarzschild solution to General Relativity applies to a stationary, spherically symmetric (uncharged) distribution of mass with asymptotically Minkowski boundary conditions for space-time. So, it basically assumes that you have a ball of stuff surrounded by empty space, and that's the type of situation where the equation for the Schwatzschild radius applies.

If we accept the idea that we can approximate the universe by a uniform distribution of matter on a large enough scale (and this is, perhaps, debatable), the Schwarzschild solution doesn't apply. But you can solve GR for this situation and what you get is the Friedman-Robertson-Walker [wikipedia.org] metric, which doesn't have any sort of event horizon, no matter how dense the matter within. Of course, it does have the interesting feature of expansion (or contraction) which lead to the beginning of modern cosmology.

It is interesting, though, if the numbers for the mass and radius of the observable universe come out that way. Perhaps it has some import, but I can't say what it is offhand (but then I don't study GR). My first guess would be that it has to do with the universe being approximately flat, but I don't think that's actually true (because that should depend on the density, Hubble's constant, and the cosmological constant).

Photons cannot escape because they are red-shifted due to time dilation. This means that the horizon will vary depending on the level of energy trying to escape it. For example, an X-ray might escape where an infra-red photon wouldn't. All or part of a huge energy blast may or may not escape, depending on its frequency, level and position. Whether it would affect the hole itself seems problematic.

Uh, no. An X-ray photon and an infra-red photon have the same velocity, c. They have different frequencies. Neither will escape a black hole, which is pretty much defined as a body having an escape velocity greater than c.

The event horizon is... the place where the escape velocity equals the speed of light.

Ding ding ding - we have a winner. This is the point that so many cosmology shows on Discovery Channel or Science Channel (or whatever) completely fail to mention; they keep describing black holes as "so massive, even light can't escape" without explaining why (Michio Kaku, Alex Fillipenko, (sp) I'm looking at you). See Wikipedia [wikipedia.org] for the details, but the important point is that escape velocity is dependent on an object's mass divided by its radius. So if mass goes high enough, or radius low enough, you get an escape velocity greater than the speed of light: AKA an event horizon.

Say it again, and remember it later:The event horizon is... the place where the escape velocity equals the speed of light.

Suppose you were falling into a black hole, and you didn't get turned into spaghetti (as might be possible if you're approaching the event horizon of a supermassive black hole). Would the event horizon seem to retreat before you? I mean, light can't escape a black hole's event horizon as we see it, but if you're falling in, wouldn't you be able to see further into the black hole as you fall?

Due to time dilation, it takes a seemingly infinite amount of time to reach an event horizon because your speed will approach the speed of light. So it is impossible for an observer to reach an event horizon without an infinite amount of time.

Suppose you were falling into a black hole, and you didn't get turned into spaghetti (as might be possible if you're approaching the event horizon of a supermassive black hole). Would the event horizon seem to retreat before you? I mean, light can't escape a black hole's event horizon as we see it, but if you're falling in, wouldn't you be able to see further into the black hole as you fall?

--PM

Well, since sight depends on light reflecting off of objects to work... No, as you approached the event horizon, you still wouldn't be able to see into the black hole, as no light would be escaping (hence no visual information conveyed).

As to other point, no, the event horizon would not appear to be receding. You would seem to be approaching it normally (from your perspective), however due to time dilation, the rest of the universe would seem to be aging quite rapidly compared to you.

I understand that this is important science, but what a weird gap in scientific knowledge when we are considering how to collapse a black hole when we can't stop the damn oil leak. Maybe we should get some of these guys involved.

Most of the calculations about black hole are based on steady state. However, the time it takes to reach this state is of order of event horizon size divided by speed of light. Larger the black hole, larger the time. Thus if you have a black hole of the size of our visible physical universe, it can take billions of years to reach steady state. During this billions of years, life can go on normally! In fact the equation of universe with omega greater than one (which means that the whole universe would eventu

however I will argue that to make it work it may end up being a matter of trying to collide two black holes into each other with great speed. Further that though I wouldn't be surprised if that speed ends up being c.

I'm guessing you'd cause the black hole to eject particles that hopefully would be structured enough to provide us with information about what's happening beyond the event horizon or they might be completely random and tell us nothing. The summary and the article itself seem very confused. They portray the event horizon like it's some kind of shell that surrounds the core of the black hole hiding it from view. The event horizon is more like an asymmetric field that you need to find the right frequency to

If you are inside an event horizon (you can't ever see anything outside of the event horizon),then if something enters your event horizon you are now able to see it, thusinvalidating the premise of the event horizon.

That means either:

1) Event horizon's do not exist.2) You can't *really* enter an event horizon from the outside.

The title of the paper is "Destroying black holes with test bodies," and the language about "destroying" black holes is echoed in both the arxiv blog summary and the/. summary. This may be somewhat misleading. They're actually talking about processes that would strip away the event horizon, leaving behind a naked singularity. The black hole wouldn't have been "destroyed," but just changed into a different form. The authors themselves put the word "destroying" in quotes in the paper.

The paper doesn't settle this one way or the other. It says shows that if you use a certain set of approximations, the result is that the event horizon can go away. However, there is no particular reason to believe that the approximation is correct.

The real issue here isn't whether a black hole can actually be transformed this way, it's the question of whether cosmic censorship [wikipedia.org] holds. If cosmic censorship fails, then general relativity is fundamentally flawed as a classical field theory, because it fails to make predictions. John Earman's famous way of expressing this is that anything could come out of a naked singularity: lost socks, green slime, even horrible things like Nixon's "Checkers" speech or Japanese monster-movie creatures.

I did Ph.D. research on this exact subject a decade ago, and at a quick glance I didn't see anything new in this paper. A spinning and/or charged black hole in theory can be spun or charged to the point where a naked singularity would appear. But, the harder you spin/charge the black hole, the harder it tries to neutralize itself by preferentially emitting particles of a given angular momentum or charge. So the equality probably is a physical limit. I thought someone had proven that years ago, but I've been out of the field for a while.

This looks kind of like someone wrote a paper so they could go to a conference or something. There doesn't appear to be anything earth-shattering (or black hole-shattering) here.

There are a number of factors to overcome when making singularity porn:

1. once you put it in, it's a real bitch to take it back out2. nobody has ever successfully pulled out in time3. they start at sucking and never manage to make it to the sex part4. Ebony has a trademark on the term "black hole"5. it's kind of a tease to watch because as much as they constantly approach the "event horizon", they never quite reach it

People thought communicators were way to far out too when TOS came out. Now we takethem for granted.

Now I don't think there are going to be any practical experiments around this theoryanytime soon but "this shit" has to start somewhere. It's been said many times beforeon/. but I'll go ahead and repeat it; a lot of scientists are heavily inspired byscience fiction and, especially when they are young, love to see if their favoritetech from their favorite shows are feasible.

Exactly. Same thing with light sabers, and now you can buy one online for $200, and go start carving people up (albeit a bit slowly with this generation... the next generation should pretty much have nailed the tecnology though, just as cell phones are not quite communicators capable of reaching our orbital ships).

If by next generation you mean the next generation of the human species... There is this annoying problem with lasers that they tend to not really stop until they hit something. Make them as powerful as you want, until we crack how to make light "expire" any time you fire up your human slicer/dicer it will also slice/dice whatever else is around you too. Perhaps one case where a glass house is a good idea. And then, we need it form a beam that behaves as a force field and/or solid object (to allow for dr

I'd say that given they can burn flesh now, they are probably only 10x power from carving through it. Ending the beam seems like a job for a transparent length of carbon nanotube fibers ending in a dispersant point (or reflectors if you want to conserve power). Really, the engineering problems seem entirely solvable at this point (expensively), and the cost will be coming down fast.

It makes sense, but seems overly impractical due to the sheer energy or mass involved with a black hole. It'd be fun to see what would happen if the static forces were able to push photons hard enough to kick them out of the gravity well. I don't buy the bit about angular momentum so readily, I think the mass would then need to be flying off the sides of the black hole ~ impractical to get that much kinetic energy when you're adding more mass.

I don't think we're talking about black holes measured in solar masses. However, if it's possible for a naked black hole to exist, we might be able to feed and disrobe a small primordial black hole or micro black hole formed through high energy collisions.

Thing 2: How is this a good thing to do? Aren't they basically stating that they don't understand how or why this is occurring, but they want to destroy something to figure out what goes on behind it? When are they planning to do this? December 21st, 2012?

They're scientists and engineers. "Break something to see how it works" is how scientists and engineers of all walks of life think. They're just thinking bigger than most. I gotta salute them for that.

It's been theorized that the universe is crawling with rogue primordial black holes. Hell some people even think the Tunguska event was caused by a black hole.

Obviously we're not going to be able to carry out this experiment in the next decade, but if we ever manage to sustained space exploration, finding and feeding a small black hole might be high on the list of experiments.

Well think of what the military types are thinking. If this device can destroy a black hole, Imagine what it can do if used on our enemies.

I am thinking if this device can destroy a black hole, this planet we are on would also be destroyed if the device was used here.

How about we get space travel to be a common as walking across the room. Then we get people (from Earth) living on different planets and living long term on space ships. Then we find an out of the way black hole to try this on. By the time we c

Thing 1: We don't know what lies behind the event horizon, since nothing (no light, no radio waves, no physical objects, no information) can come out. It's a one-way gate. Theory is all well and good, but the only way to find out for sure what is on the other side would be to remove or disrupt the event horizon. Scientists by their very nature aren't the kind of people who can fail to see what's inside a black hole, given the opportunity.

Fret not, young one, this is just how things get done. You see, the whole damn universe was written in COBOL and we don't have the source code so any module we don't understand has to be disassembled. Hopefully, after disassembly we'll be able to make some sense out of what's going on. Once we understand everything in the universe, we can re-write it in Erlang.

Well, theoretically, (unless the theory has changed) during the big bang matter could have been compressed past the Swartzschild radius due to pressure and black-holes formed that mass much less than is required for a black hole to form today from gravity alone. http://en.wikipedia.org/wiki/Primordial_black_hole [wikipedia.org] Most of these will have evaporated by now (or maybe not depending on how you interpret the string theory), but if they can exist there should still be a great many of these in the universe. We kno

Well, theoretically, (unless the theory has changed) during the big bang matter could have been compressed past the Swartzschild radius due to pressure and black-holes formed that mass much less than is required for a black hole to form today from gravity alone. http://en.wikipedia.org/wiki/Primordial_black_hole [wikipedia.org] Most of these will have evaporated by now (or maybe not depending on how you interpret the string theory), but if they can exist there should still be a great many of these in the universe. We know that a black hole can carry a charge, and the surface gravity can be calculated. It is possible that there may be some of these in the solar system, perhaps in many years we will discover a way to detect them, and increase their charge to the point where they could be manipulated electromagnetically.

I love a sentence that can be misinterpreted to imply that I can retroactively change the workings of the universe based on my presumably mutable interpretation of a theory. I'm sure magic works just like this.

Although no one knows what happens at the end point of black hole evaporation it is unlikely it would leave a naked singularity since the mass of the singularity is what is being 'evaporated'. Besides, even if there was a naked singularity around just before the thing evaporates it would be kicking out so much energy you wouldn't be able to get anywhere near it. A 1kg black hole evaporating would release the equivalent energy to a large thermonuclear weapon in a fraction of a second.

That allows information from inside the event horizon to leak outside (which is all the astrophysicists really need) and allows the evaporation of black holes, but the event horizon would remain intact. However, we have never seen Hawking Radiation (yet) and it depends some on certain assumptions being valid. One of these assumptions is that the singularity is something "physical".

A lot of cosmologists don't like infinities, so don't like singularities, but let us consider what "infinite gravity" would actually mean. It would mean you have a vertical gravitational well, with the universe being the "walls" of this well. As far as the universe is concerned. the actual hole that makes up the interesting part of the well is on the outside, just as the air in a physical well is outside the brick lining that comprise the walls. Since what we call "physical" are the objects inside the universe, it makes no logical or rational sense to talk of something that is on the outside as being "physical". You can detect it using the usual rules of topology and geometry (you can't apply any topological transformation to a torus to produce a sphere), but if you picture yourself as a Flatlander on the surface of said torus, you could NEVER observe the region on the outside that distinguishes the torus from a sphere. You could infer it existed, you could even prove that it has certain properties, but that's it.

Cosmologists and topologists don't get along, which is why space/time existed as fact in geometry long, long before any physicist accepted it was real. Einstein is said to have loathed and despised the concept, and only grudgingly accepted it had to be true after being dragged, kicking and screaming, by his theories into reaching no other answer. (You might gather from this I have a low opinion of certain branches of physics.)

But precisely because the rules of topology FORBID a torus to become a sphere, it would be impossible for a genuinely infinite-gravity singularity to evaporate completely. Instead of their evaporation speeding up as they shrank, it would have to slow down -- if they evaporated at all. Entirely the opposite of what physics expects. There's no reason for them TO evaporate, however. It is only required in cosmology to meet the requirements of the 2nd Law of Thermodynamics, but thermodynamics only applies to what exists. A hole is a region where the walls do NOT exist.

There is a third possibility. Under the standard model for space/time, time is orthogonal to space. If space is bent at 90' to all other spacial dimensions, then it is no longer space. It is time. This means that not only is there a singularity at the heart of every black hole, it would be the SAME singularity. There would have only ever been one singularity, right at T=0, and the throats of all black holes would be directly and permanently hard-linked to this. There would still be no evaporation at this end of time (it has already happened).

A fourth (and fifth) possibility is that black holes never actually form at all. There's an entire alternative model in cosmology which prohibits them outright, giving you that fourth option. Then, Professor Hawking's work on imaginary time and the curvature of time around singularities would eliminate the need for a singularity outright. If you factor time curving as well as space, then space/time never vanishes to a point. Space/time would become parabolic, giving it a minimal state, but there is no moment in which any variable hits zero or any infinite states are achieved.

There's probably others I've either not heard of, or have heard of and forgotten. But at least five different ways DO exist and are recognized in modern physics as possible in which no black hole singularity of the kind imagined would arise. That means there is simply no theoretical ground (right now) to assume that this new theory has any meaning or would make any sense.

Maybe by the time anything reaches the singularity, the universe would've ended and time would cease to exist. That is, you can never reach a singularity, you (or what's left of you) can only ever continue to spiral around it until literally the end of time.

"Charge and angular momentum" aren't that hard to come by near supermassive black holes, after all - massive accretion disk certainly can add angular momentum; and with large part of it being ionized one way or another, we might have appropriate charge in some cases...

What if naked singularity would turn out to be behind quasars; generally some unusually active cores of galaxies or relativistic jets?

Peel back an Event Horizon? Get blasted with Radiation/Exotic particles,etc... Um just think what happens to the axis area... They are evaporating just not in a observable curvature that we can understand or detect.

Not true. we might be able to create a microscopic black hole that is massive enough to exist long enough that we could attempt this and observe the result. But you are right that attempting it on a natural black hole is pretty much impossible.